This invention relates to a process for production of a cyclohexylamine by the catalytic hydrogenation of the corresponding aromatic amine.
The use of ruthenium catalysts in hydrogenating aromatic compounds to produce cyclohexylamines is disclosed in U.S. Pat. No. 2,606,925, in the name of Gerald M. Whitman. This patent shows the reaction of an aromatic compound containing a nitrogen atom attached to the aromatic ring with hydrogen under pressure over a variety of ruthenium catalysts. Pressures of from 1,000 to 10,000 pounds per square inch (6.9 to 69 MPa) are generally used, with temperatures from 20.degree. to 150.degree. C. Typical reactions produced 75% of theoretical yield of the desired cyclohexylamine.
Continuous hydrogenation of aniline to produce cyclohexylamine using a ruthenium catalyst is taught in U.S. Pat. No. 2,822,392, to G. M. Illich et al. Patentees use a temperature of from 200.degree. to 250.degree. C. and hydrogen pressures of from 250 to 10,000 psi (1.7 to 69 MPa). The inclusion of up to 20 volume percent of dicyclohexylamine in the aniline feed, or 1.5-3% by volume of NH.sub.3 is recommended. However, no significant improvement is shown in the examples by adding NH.sub.3, and the process is said to be inoperative at temperatures below 200.degree. C.
In an article by H. Greenfield (J. Org. Chem. 29, 3082 (1964), a batch hydrogenation of aniline using a ruthenium catalyst is reported. The inclusion of NH.sub.3 is said to inhibit the ruthenium catalyst, and the reaction at 145.degree. C. is shown to be impractically slow, and to produce significant quantities of undesirable dicyclohexylamine.